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packages/petitparser/lib/src/petitparser/parser.dart

+part of petitparser;
+
+/// Abstract base class of all parsers.
+abstract class Parser {
+
+  /// Primitive method doing the actual parsing.
+  ///
+  /// The method is overridden in concrete subclasses to implement the
+  /// parser specific logic. The methods takes a parse [context] and
+  /// returns the resulting context, which is either a [Success] or
+  /// [Failure] context.
+  Result parseOn(Context context);
+
+  /// Returns the parse result of the [input].
+  ///
+  /// The implementation creates a default parse context on the input and calls
+  /// the internal parsing logic of the receiving parser.
+  ///
+  /// For example, `letter().plus().parse('abc')` results in an instance of
+  /// [Success], where [Result.position] is `3` and [Success.value] is
+  /// `[a, b, c]`.
+  ///
+  /// Similarly, `letter().plus().parse('123')` results in an instance of
+  /// [Failure], where [Result.position] is `0` and [Failure.message] is
+  /// ['letter expected'].
+  Result parse(input) {
+    return parseOn(new Context(input, 0));
+  }
+
+  /// Tests if the [input] can be successfully parsed.
+  ///
+  /// For example, `letter().plus().accept('abc')` returns `true`, and
+  /// `letter().plus().accept('123')` returns `false`.
+  bool accept(input) {
+    return parse(input).isSuccess;
+  }
+
+  /// Returns a list of all successful overlapping parses of the [input].
+  ///
+  /// For example, `letter().plus().matches('abc de')` results in the list
+  /// `[['a', 'b', 'c'], ['b', 'c'], ['c'], ['d', 'e'], ['e']]`. See
+  /// [Parser.matchesSkipping] to retrieve non-overlapping parse results.
+  Iterable matches(input) {
+    var list = new List();
+    and()
+        .map((each) => list.add(each))
+        .seq(any())
+        .or(any())
+        .star()
+        .parse(input);
+    return list;
+  }
+
+  /// Returns a list of all successful non-overlapping parses of the input.
+  ///
+  /// For example, `letter().plus().matchesSkipping('abc de')` results in the
+  /// list `[['a', 'b', 'c'], ['d', 'e']]`. See [Parser.matches] to retrieve
+  /// overlapping parse results.
+  Iterable matchesSkipping(input) {
+    var list = new List();
+    map((each) => list.add(each)).or(any()).star().parse(input);
+    return list;
+  }
+
+  /// Returns new parser that accepts the receiver, if possible. The resulting
+  /// parser returns the result of the receiver, or `null` if not applicable.
+  /// The returned value can be provided as an optional argument [otherwise].
+  ///
+  /// For example, the parser `letter().optional()` accepts a letter as input
+  /// and returns that letter. When given something else the parser succeeds as
+  /// well, does not consume anything and returns `null`.
+  Parser optional([otherwise]) => new OptionalParser(this, otherwise);
+
+  /// Returns a parser that accepts the receiver zero or more times. The
+  /// resulting parser returns a list of the parse results of the receiver.
+  ///
+  /// This is a greedy and blind implementation that tries to consume as much
+  /// input as possible and that does not consider what comes afterwards.
+  ///
+  /// For example, the parser `letter().star()` accepts the empty string or
+  /// any sequence of letters and returns a possibly empty list of the parsed
+  /// letters.
+  Parser star() => repeat(0, unbounded);
+
+  /// Returns a parser that parses the receiver zero or more times until it
+  /// reaches a [limit]. This is a greedy non-blind implementation of the
+  /// [Parser.star] operator. The [limit] is not consumed.
+  Parser starGreedy(Parser limit) => repeatGreedy(limit, 0, unbounded);
+
+  /// Returns a parser that parses the receiver zero or more times until it
+  /// reaches a [limit]. This is a lazy non-blind implementation of the
+  /// [Parser.star] operator. The [limit] is not consumed.
+  Parser starLazy(Parser limit) => repeatLazy(limit, 0, unbounded);
+
+  /// Returns a parser that accepts the receiver one or more times. The
+  /// resulting parser returns a list of the parse results of the receiver.
+  ///
+  /// This is a greedy and blind implementation that tries to consume as much
+  /// input as possible and that does not consider what comes afterwards.
+  ///
+  /// For example, the parser `letter().plus()` accepts any sequence of
+  /// letters and returns a list of the parsed letters.
+  Parser plus() => repeat(1, unbounded);
+
+  /// Returns a parser that parses the receiver one or more times until it
+  /// reaches [limit]. This is a greedy non-blind implementation of the
+  /// [Parser.plus] operator. The [limit] is not consumed.
+  Parser plusGreedy(Parser limit) => repeatGreedy(limit, 1, unbounded);
+
+  /// Returns a parser that parses the receiver one or more times until it
+  /// reaches a [limit]. This is a lazy non-blind implementation of the
+  /// [Parser.plus] operator. The [limit] is not consumed.
+  Parser plusLazy(Parser limit) => repeatLazy(limit, 1, unbounded);
+
+  /// Returns a parser that accepts the receiver between [min] and [max] times.
+  /// The resulting parser returns a list of the parse results of the receiver.
+  ///
+  /// This is a greedy and blind implementation that tries to consume as much
+  /// input as possible and that does not consider what comes afterwards.
+  ///
+  /// For example, the parser `letter().repeat(2, 4)` accepts a sequence of
+  /// two, three, or four letters and returns the accepted letters as a list.
+  Parser repeat(int min, int max) {
+    return new PossessiveRepeatingParser(this, min, max);
+  }
+
+  /// Returns a parser that parses the receiver at least [min] and at most [max]
+  /// times until it reaches a [limit]. This is a greedy non-blind implementation of
+  /// the [Parser.repeat] operator. The [limit] is not consumed.
+  Parser repeatGreedy(Parser limit, int min, int max) {
+    return new GreedyRepeatingParser(this, limit, min, max);
+  }
+
+  /// Returns a parser that parses the receiver at least [min] and at most [max]
+  /// times until it reaches a [limit]. This is a lazy non-blind implementation of
+  /// the [Parser.repeat] operator. The [limit] is not consumed.
+  Parser repeatLazy(Parser limit, int min, int max) {
+    return new LazyRepeatingParser(this, limit, min, max);
+  }
+
+  /// Returns a parser that accepts the receiver exactly [count] times. The
+  /// resulting parser returns a list of the parse results of the receiver.
+  ///
+  /// For example, the parser `letter().times(2)` accepts two letters and
+  /// returns a list of the two parsed letters.
+  Parser times(int count) => repeat(count, count);
+
+  /// Returns a parser that accepts the receiver followed by [other]. The
+  /// resulting parser returns a list of the parse result of the receiver
+  /// followed by the parse result of [other]. Calling this method on an
+  /// existing sequence code not nest this sequence into a new one, but
+  /// instead augments the existing sequence with [other].
+  ///
+  /// For example, the parser `letter().seq(digit()).seq(letter())` accepts a
+  /// letter followed by a digit and another letter. The parse result of the
+  /// input string `'a1b'` is the list `['a', '1', 'b']`.
+  Parser seq(Parser other) => new SequenceParser([this, other]);
+
+  /// Convenience operator returning a parser that accepts the receiver followed
+  /// by [other]. See [Parser.seq] for details.
+  Parser operator &(Parser other) => this.seq(other);
+
+  /// Returns a parser that accepts the receiver or [other]. The resulting
+  /// parser returns the parse result of the receiver, if the receiver fails
+  /// it returns the parse result of [other] (exclusive ordered choice).
+  ///
+  /// For example, the parser `letter().or(digit())` accepts a letter or a
+  /// digit. An example where the order matters is the following choice between
+  /// overlapping parsers: `letter().or(char('a'))`. In the example the parser
+  /// `char('a')` will never be activated, because the input is always consumed
+  /// `letter()`. This can be problematic if the author intended to attach a
+  /// production action to `char('a')`.
+  Parser or(Parser other) => new ChoiceParser([this, other]);
+
+  /// Convenience operator returning a parser that accepts the receiver or
+  /// [other]. See [Parser.or] for details.
+  Parser operator |(Parser other) => this.or(other);
+
+  /// Returns a parser (logical and-predicate) that succeeds whenever the
+  /// receiver does, but never consumes input.
+  ///
+  /// For example, the parser `char('_').and().seq(identifier)` accepts
+  /// identifiers that start with an underscore character. Since the predicate
+  /// does not consume accepted input, the parser `identifier` is given the
+  /// ability to process the complete identifier.
+  Parser and() => new AndParser(this);
+
+  /// Returns a parser (logical not-predicate) that succeeds whenever the
+  /// receiver fails, but never consumes input.
+  ///
+  /// For example, the parser `char('_').not().seq(identifier)` accepts
+  /// identifiers that do not start with an underscore character. If the parser
+  /// `char('_')` accepts the input, the negation and subsequently the
+  /// complete parser fails. Otherwise the parser `identifier` is given the
+  /// ability to process the complete identifier.
+  Parser not([String message]) => new NotParser(this, message);
+
+  /// Returns a parser that consumes any input token (character), but the
+  /// receiver.
+  ///
+  /// For example, the parser `letter().neg()` accepts any input but a letter.
+  /// The parser fails for inputs like `'a'` or `'Z'`, but succeeds for
+  /// input like `'1'`, `'_'` or `'$'`.
+  Parser neg([String message]) => not(message).seq(any()).pick(1);
+
+  /// Returns a parser that discards the result of the receiver, and returns
+  /// a sub-string of the consumed range in the string/list being parsed.
+  ///
+  /// For example, the parser `letter().plus().flatten()` returns `'abc'`
+  /// for the input `'abc'`. In contrast, the parser `letter().plus()` would
+  /// return `['a', 'b', 'c']` for the same input instead.
+  Parser flatten() => new FlattenParser(this);
+
+  /// Returns a parser that returns a [Token]. The token carries the parsed
+  /// value of the receiver [Token.value], as well as the consumed input
+  /// [Token.input] from [Token.start] to [Token.stop] of the input being
+  /// parsed.
+  ///
+  /// For example, the parser `letter().plus().token()` returns the token
+  /// `Token[start: 0, stop: 3, value: abc]` for the input `'abc'`.
+  Parser token() => new TokenParser(this);
+
+  /// Returns a parser that consumes input before and after the receiver. The
+  /// optional argument is a parser that consumes the excess input. By default
+  /// `whitespace()` is used. Two arguments can be provided to have different
+  /// parsers on the [left] and [right] side.
+  ///
+  /// For example, the parser `letter().plus().trim()` returns `['a', 'b']`
+  /// for the input `' ab\n'` and consumes the complete input string.
+  Parser trim([Parser left, Parser right]) {
+    if (left == null) left = whitespace();
+    if (right == null) right = left;
+    return new TrimmingParser(this, left, right);
+  }
+
+  /// Returns a parser that succeeds only if the receiver consumes the complete
+  /// input, otherwise return a failure with the optional [message].
+  ///
+  /// For example, the parser `letter().end()` succeeds on the input `'a'`
+  /// and fails on `'ab'`. In contrast the parser `letter()` alone would
+  /// succeed on both inputs, but not consume everything for the second input.
+  Parser end([String message = 'end of input expected']) {
+    return new EndOfInputParser(this, message);
+  }
+
+  /// Returns a parser that points to the receiver, but can be changed to point
+  /// to something else at a later point in time.
+  ///
+  /// For example, the parser `letter().settable()` behaves exactly the same
+  /// as `letter()`, but it can be replaced with another parser using
+  /// [SettableParser.set].
+  SettableParser settable() => new SettableParser(this);
+
+  /// Returns a parser that evaluates a [function] as the production action
+  /// on success of the receiver.
+  ///
+  /// For example, the parser `digit().map((char) => int.parse(char))` returns
+  /// the number `1` for the input string `'1'`. If the delegate fail, the
+  /// production action is not executed and the failure is passed on.
+  Parser map(Function function) => new ActionParser(this, function);
+
+  /// Returns a parser that transform a successful parse result by returning
+  /// the element at [index] of a list. A negative index can be used to access
+  /// the elements from the back of the list.
+  ///
+  /// For example, the parser `letter().star().pick(-1)` returns the last
+  /// letter parsed. For the input `'abc'` it returns `'c'`.
+  Parser pick(int index) {
+    return this.map((List list) {
+      return list[index < 0 ? list.length + index : index];
+    });
+  }
+
+  /// Returns a parser that transforms a successful parse result by returning
+  /// the permuted elements at [indexes] of a list. Negative indexes can be
+  /// used to access the elements from the back of the list.
+  ///
+  /// For example, the parser `letter().star().permute([0, -1])` returns the
+  /// first and last letter parsed. For the input `'abc'` it returns
+  /// `['a', 'c']`.
+  Parser permute(List<int> indexes) {
+    return this.map((List list) {
+      return indexes.map((index) {
+        return list[index < 0 ? list.length + index : index];
+      }).toList();
+    });
+  }
+
+  /// Returns a parser that consumes the receiver one or more times separated
+  /// by the [separator] parser. The resulting parser returns a flat list of
+  /// the parse results of the receiver interleaved with the parse result of the
+  /// separator parser.
+  ///
+  /// If the optional argument [includeSeparators] is set to `false`, then the
+  /// separators are not included in the parse result. If the optional argument
+  /// [optionalSeparatorAtEnd] is set to `true` the parser also accepts an
+  /// optional separator at the end.
+  ///
+  /// For example, the parser `digit().separatedBy(char('-'))` returns a parser
+  /// that consumes input like `'1-2-3'` and returns a list of the elements and
+  /// separators: `['1', '-', '2', '-', '3']`.
+  Parser separatedBy(Parser separator,
+      {bool includeSeparators: true, bool optionalSeparatorAtEnd: false}) {
+    var repeater = new SequenceParser([separator, this]).star();
+    var parser = new SequenceParser(optionalSeparatorAtEnd
+        ? [this, repeater, separator.optional(separator)]
+        : [this, repeater]);
+    return parser.map((List list) {
+      var result = new List();
+      result.add(list[0]);
+      for (var tuple in list[1]) {
+        if (includeSeparators) {
+          result.add(tuple[0]);
+        }
+        result.add(tuple[1]);
+      }
+      if (includeSeparators &&
+          optionalSeparatorAtEnd &&
+          !identical(list[2], separator)) {
+        result.add(list[2]);
+      }
+      return result;
+    });
+  }
+
+  /// Returns a shallow copy of the receiver.
+  ///
+  /// Override this method in all subclasses.
+  Parser copy();
+
+  /// Recursively tests for structural equality of two parsers.
+  ///
+  /// The code can automatically deals with recursive parsers and parsers that
+  /// refer to other parsers. This code is supposed to be overridden by parsers
+  /// that add other state.
+  bool isEqualTo(Parser other, [Set<Parser> seen]) {
+    if (seen == null) {
+      seen = new Set();
+    }
+    if (this == other || seen.contains(this)) {
+      return true;
+    }
+    seen.add(this);
+    return runtimeType == other.runtimeType &&
+        hasEqualProperties(other) &&
+        hasEqualChildren(other, seen);
+  }
+
+  /// Compare the properties of two parsers. Normally this method should not be
+  /// called directly, instead use [Parser#equals].
+  ///
+  /// Override this method in all subclasses that add new state.
+  bool hasEqualProperties(Parser other) => true;
+
+  /// Compare the children of two parsers. Normally this method should not be
+  /// called directly, instead use [Parser#equals].
+  ///
+  /// Normally this method does not need to be overridden, as this method works
+  /// generically on the returned [Parser#children].
+  bool hasEqualChildren(Parser other, Set<Parser> seen) {
+    var thisChildren = children,
+        otherChildren = other.children;
+    if (thisChildren.length != otherChildren.length) {
+      return false;
+    }
+    for (var i = 0; i < thisChildren.length; i++) {
+      if (!thisChildren[i].isEqualTo(otherChildren[i], seen)) {
+        return false;
+      }
+    }
+    return true;
+  }
+
+  /// Returns a list of directly referenced parsers.
+  ///
+  /// For example, `letter().children` returns the empty collection `[]`,
+  /// because the letter parser is a primitive or leaf parser that does not
+  /// depend or call any other parser.
+  ///
+  /// In contrast, `letter().or(digit()).children` returns a collection
+  /// containing both the `letter()` and `digit()` parser.
+  List<Parser> get children => const [];
+
+  /// Changes the receiver by replacing [source] with [target]. Does nothing
+  /// if [source] does not exist in [Parser.children].
+  ///
+  /// The following example creates a letter parser and then defines a parser
+  /// called `example` that accepts one or more letters. Eventually the parser
+  /// `example` is modified by replacing the `letter` parser with a new
+  /// parser that accepts a digit. The resulting `example` parser accepts one
+  /// or more digits.
+  ///
+  ///     var letter = letter();
+  ///     var example = letter.plus();
+  ///     example.replace(letter, digit());
+  void replace(Parser source, Parser target) {
+    // no children, nothing to do
+  }
+}